For the elimination of malodorous and/or harmful gaseous components, methods and apparatuses are known which comprise passing a gas containing malodorous and/or harmful components through a bed of granular or fibrous activated carbon. Such malodorous or harmful gases may contain sulfur-containing compounds such as hydrogen sulfide, mercaptans and sulfides, nitrogen-containing compounds such as ammonia and amines, aldehydes, carboxylic acids, hydrocarbons and the like.
These malodorous and harmful gaseous components are usually present in very low concentrations in the atmosphere but with the above-mentioned activated carbon alone, it is difficult to selectively adsorb and remove all of these malodorous and harmful components. The rate and amount of elimination are also very meager. Therefore, a large quantity of activated carbon is required for the adsorption/removal of malodorous and harmful components. Furthermore, since the activated carbon bed presents a large flow resistance, it cannot smoothly remove the malodorous and harmful components, with the result that a fan is essentially required but this results in an increased electric utility cost. Replacement of deactivated carbon with a fresh supply is also complicated.
For the adsorption/elimination of a plurality of malodorous and harmful components, chemical-supporting activated carbon species have been proposed. Thus, Japanese Patent laid open No. 151963/1984 discloses, as an acid-supporting activated carbon species, citric acid- or alkali metal citrate-supporting activated carbon. Japanese Patent laid open No. 227704/1984 proposes activated carbon supporting 1 to 20% by weight of a phosphoric acid compound. Furthermore, Japanese Patent laid open No. 172561/1986 discloses a deodorizer in the form of a honeycomb molding or the like which comprises 50 to 93% by weight of activated carbon, 5 to 30% by weight of a solid acid and 2 to 20% by weight of an organic binder.
However, such acid-supporting activated carbon species are low in adsorptivity for sulfur-containing compounds such as hydrogen sulfide and mercaptans.
Japanese Patent laid open No. 262742/1987 proposes a chemical-supporting activated carbon honeycomb supporting an acid, an alkali or a weakly acidic chemical such as an iron halide. Japanese Patent laid open No. 63882/1977 describes activated carbon supporting 0.1 to 2% by weight of an acid or alkali. Such honeycomb, when it is supporting an acid chemical such as sulfuric acid, can remove ammonia, while it is able to remove hydrogen sulfide and the like when an alkaline chemical is supported.
However, when an acid or weakly acidic chemical and an alkali are simultaneously supported on activated carbon, a salt is formed and therefore the acid and alkali fail to perform their respective functions, with the result that the adsorptivities for both nitrogen-containing compounds and sulfur-containing compounds are markedly reduced. For this reason, acid-supporting activated carbon and alkali-supporting activated carbon should be used separately. Furthermore, supporting of an alkaline chemical to eliminate sulfur-containing compounds such as hydrogen sulfide results in a lowered flash point, thus causing troubles in practical use. On the other hand, the addition of a flame retardant leads to a decrease in the amount of adsorption per unit specific surface area and, hence, a decrease in adsorption efficiency.
Iodine- or iodine compound-supporting activated carbon is also known in the art. Thus, British Patent No. 1090306, for instance, describes iodine- or ammonium iodide-supporting activated carbon and Japanese Patent Publication No. 9377/1987 discloses a deodorizer comprising an oxide and/or oxo acid of iodine supported on activated carbon. However, when iodine or such an iodine compound is used singly, the ability to remove ammonia and amines is insufficient and, hence, ordinary gases containing a plurality of malodorous components cannot be deodorized.
Thus, with such chemical-supporting activated carbon species and honeycombs made therefrom, harmful components which can be adsorbed and removed are limited by the type of chemical supported. Therefore, it is difficult to adsorb and remove a variety of malodorous and harmful components simultaneously with sufficient efficiency with one single activated carbon species over a long period of time.
Activated carbon supporting iodine or an iodine compound together with phosphoric acid is also known in the art. Thus, Japanese Patent laid open No. 131847/1975 (Japanese Patent Publication No. 2368/1982) proposes activated carbon supporting iodine or an iodine compound together with boric acid or phosphoric acid, both supported thereon. This activated carbon supports 0.2 to 4 g of phosphoric acid on 100 g of activated carbon (corresponding to 0.06 to 1.22 mg equivalents of phosphoric acid/g of activated carbon).
However, the intended purposes of said activated carbon are to remove sulfur compounds such as hydrogen sulfide and methylmercaptan, to regenerate iodine- or iodine compound-supporting activated carbon and to prevent the iodine or iodine compound from dropping off in the treatment for regeneration. Simultaneous elimination of a plurality of malodorous components is not intended at all. In fact, when the above-mentioned specific amount of phosphoric acid is supported simultaneously, the adsorptivity of the iodine or iodine compound decreases markedly in a short period of time. In addition, in spite of the supporting of phosphoric acid, it is impossible to adsorb and remove nitrogen-containing compounds such as ammonia and amines for a long period of time. It is a common knowledge in the art that supporting of phosphoric acid results in decreased adsorptivity of iodine or iodine compounds. For that reason, studies so far made regarding the amount of phosphoric acid to be supported are limited to an amount thereof just required to prevent the iodine or iodine compound from dropping off and enable activated carbon regeneration. No consideration has been given as yet to larger amount of phosphoric acid.
Japanese Patent laid open No. 68136/1986 discloses an adsorbent comprising activated carbon with sulfuric acid and an oxo acid of iodine both supported thereon, which is the only example so far disclosed of activated carbon for adsorption and elimination of ammonia and the like as well as sulfur compounds.
However, this adsorbent had a very low ignition point resulting from the supporting of sulfuric acid. In addition, this activated carbon adsorbent allows the oxo acid of iodine to be lost therefrom in the form of hydrogen iodide and, as a result, its adsorptivity decreases even in an early stage of use. Furthermore, drying of the adsorbent may cause odor development, an irritating odor may emanate during use and, further, the container containing the adsorbent may be corroded. Therefore, it is very difficult to apply such adsorbent to an ordinary inhabited area.
The adsorbent mentioned above, where an oxo acid of iodine (an iodine compound) and sulfuric acid (a member of the class of inorganic acids to which phosphoric acid also belongs) are supported, might be expected to be high in the ability to adsorb and eliminate sulfur-containing compounds such as hydrogen sulfide and methylmercaptan, like the earlier mentioned activated carbon supporting an iodine compound and phosphoric acid. Contrary to this expectation, the adsorptivity of this adsorbent for sulfur-containing compounds is low and moreover shows a marked decrease in a short period of time.
Thus, when two chemicals differing in kind are supported on activated carbon, one chemical lowers the eliminating ability of the other. Therefore, it is generally difficult to adsorb and remove a variety of malodorous and harmful components over a long period of time by supporting chemicals differing in kind combinedly on activated carbon.